"I'm all for freedom of speech - but you don't have the right to shout fire in a crowded theatre."

This vulgar paraphrase of the hackneyed dictum of Judge Oliver Wendell Holmes Jr, so beloved of cliché-mongers, is interesting only in that it leaves out the most important word in the noble judge's sentence, which actually reads: "The most stringent protection of free speech would not protect a man falsely shouting fire in a theatre and causing a panic." That word is "falsely". What Wendell Holmes meant was that you don't have the right to shout fire in a crowded theatre when you know that there is no fire. This, the First Amendment would not protect.

The "falsely" bit matters, because if you do notice a fire, you surely have the right to alert people to it fairly volubly. Some people might get hurt in the ensuing stampede, but not as many people as could get scorched in the inferno.

As we are now reminded on an almost daily basis, Britain has no First Amendment. So when David Miliband used Wendell Holmes to justify the ban on Dutch MP Geert Wilders from entering the UK, it hurt for more than aesthetic reasons. "We have profound commitment to freedom of speech," said the British Foreign Secretary. Anybody hear the "but" coming?

"But there is no freedom to cry fire in a crowded theatre."

If there ever were an example of a theatre tensed for a good stampede it would be a country that has just suffered a major terrorist atrocity. So it was interesting that when he was in Mumbai in January, at the Taj Mahal Hotel, in which Islamist terrorists had just mown down scores of people, Miliband decided to use the opportunity to deny the existence of Islamist terrorism and attribute the attacks to the Indian government's behaviour over Kashmir. An Indian opposition spokesman declared: "In recent years, there has been no bigger disaster than the visit of David Miliband."

In the spirit of openness, I should state that I have a profound belief in the right of David Miliband to be a diplomatic disaster. I'm not sure I'd defend to the death his right to be a diplomatic disaster, but I certainly wouldn't try to bar him from the country for being a diplomatic disaster. I might even advise him to consider shouting "fire" in the middle of his next diplomatic disaster in the hope it will deflect people's attention from whichever diplomatic disaster he's then in the middle of. Of course, Miliband had not seen the Fitna film for which he was so desperate to keep Geert Wilders out of the UK. But he knew that it was very bad. None of the panellists on the BBC 1's Question Time had seen the film, but all of them knew that it was a nasty film and that its maker should be kept out.

The shadow Home Secretary, Chris Grayling, may or may not have seen the film, but supported the ban anyway, "if Geert Wilders has expressed views that represent a threat to public security." Which is to say: "I'm not sure if there's a fire. I'm not qualified to call that one. But if there were to be a fire then we would have a profound commitment to tackling it."

Since so many people, including the Home Secretary and the Foreign Secretary, have stampeded over the niceties of allowing British parliamentarians to sit in a room with Dutch parliamentarians, what Wilders says must be pretty bad.

I disagree with some of what Wilders says. He thinks the Koran should be banned. I think it should be discussed, debated and even denounced. But I don't think it should be banned. I can see why in the Dutch context - where Mein Kampf is banned - a case can be made. But I'm not persuaded. I also think Wilders is deeply wrong to express an interest in allying his party in any way with the Flemish nationalists of Vlaams Belang, as he did recently. However, on some of the most important issues of our time he is right.

In the next few weeks a set of well-known extremist Muslims will be touring the campuses of the UK. Bilal Philips, Kamal el-Helbawy and others will be untroubled by the Home Secretary as they make their rabble-rousing speeches. It is only those - as a growing list of people can now attest - who point to the people saying bad things that are censored.

Wilders has not called for anybody to be murdered. He has exposed the way in which violent verses in the Koran can justify violent actions by Muslims. More of a fire fighter than a fire starter, Wilders has been caught in the nightmare of a British political establishment that cannot discern the difference.

As the fire beneath our feet spreads, our politicians are now united in stopping anyone mentioning the truth about what is going on in this theatre. A stampede for the exit should be the least of their worries.